Abstract: The leak equivalent relationship between liquid and helium is an important issue to avoid the leaking of liquid medium in the sealed pipes and to improve the accuracy and reliability of leak detection. This paper studies the liquid working mediums (C2H6O2 and C6F15N) in the sealed pipes of the environment control and life protection system. The ranges for leak rate equivalent relationship between liquid and helium were theoretically analyzed. The leak rates of liquid and helium through metal aperture were measured by the technology of quantitative analysis of quadrupole mass spectrometry. The experimental results show that the leak rate equivalent relationships are all in good agreement with the theoretical predictions. The liquid leaking process involves two-phase flows, moreover, the leak rate of C2H6O2 is much less than that of helium, and the leak rate of C6F15N is more than that of the helium leak rate. The results provide a basic method and some important data for researching fluid leak and the leak equivalent relationship between liquid and gas.